Optically active D-armino acids like p-hydroxyphenylglycine and D-phenylglycine are widely used as intermediates in pharmaceutical filed for the synthesis of semisynthetic antibiotics, peptide hormones, pyrethroids and pesticides. A chemoenzymatic route for the synthesis of various D-amino acids involves the conversion of DL-5-monosubstituted hydantoins to D-amino acids via N-carbamoyl D-amino acid by producing aerobic microorganisms [Takahashi, S., Ohashi, T., Kii, Y., Kumagai, H. and Yamada, H. (1979), J. Ferment. Technol., 57, 328-332; Yokozeki, K., Nakamori, S., Eguchi, C., Yamada, K. and Mitsugi, K. (1987). Agric. Biol. chelm. 51, 355-362]. In this process a DL-5-substituted hydantoin is asymmetrically hydrolyzed to the N-carbamoyl-D-amino acid using D-specific hydantoinase (dihydropyrimidinase, EC 3.5.2.2) and the product is further chemically converted to the corresponding D-amino acids under acidic conditions.
Much attention has been directed towards the isolation, screening and selection of D-hydantoinase producing microbes [Morin, A., Hummel, W. and Kula, M. R. (1987), J. Gen Microbiol.133, 1201-1207; Kim D. M. and Kim, H. S. (1993), Enzyme Microb Technol. 15, 530-534; Kalkote, U. R., Joshi, R. R., Joshi, R. A., Ravindranathan, T., Bastawde, K. B., Gokhale, D. V. Patil, S. G., Jogdand. V. V., Gaikwad, B. G. and Nene, S. (1993) Indian Patent No. 199/DEL/1993; Gokhale, D. V., Bastawde, K. B., Patil, S. G., Kalkote, U. R., Joshi, R. R., Joshi, R. A., Ravindranathan, T., Jogdand, V. V., Gaikwad, B. G. and Nene, S. (1996). Enzyme Microb. Technl. 18, 353-357] and the characterization of the kinetic properties of the enzyme [Runser, S. M. and Ohleyer, E. (1990), Biotechnolgy Lett. 12, 259-264; Morin, A., Leblanc, D., Paleczek, A., Hummel, W. and Kula, M. R.(1990), J. Biotechnol 16, 37-48; Ogawa, J., Kaimura, T., Yamada, H. and Shinizu, S. (1994), FEMS Microbiol Lett. 122, 44-60]. One of the main problems associated with the use of enzymes for biocatalysis is their stability. A thermophilic bacterium Bacillus stearothermophilus SD-1 showing high thermostability and activity of D-hydantoinase was isolated and the enzyme was purified to its homogeneity [Lee, S. G., Lee, D. C., Hong, S. P., Sung, M. H. and Kim H. S. (1995). Appl. Microbiol. Biotechnol. 43, 270-276].